A measurement station on a stream after a 2-hour storm recorded the following discharges from a 1.2 square mile drainage area

 

Hour

Discharge (cfs)

0

102

1

99

2

101

3

215

4

507

5

625

6

455

7

325

8

205

9

145

10

100

11

70

12

55

13

49

14

43

15

38

 

Use an excel spreadsheet for this homework.  Drop it off in Blackboard.

 

Develop a 2-hour Unit Hydrograph (TAB called “Unit Hydrograph”)

 

a)     Develop the runoff hydrograph by separating the groundwater from the discharge by a straight (or sloped line)

 

b)     Develop the unit hydrograph

Hint #1:  Flow should start and end at zero cfs

Hint #2: The area under the unit hydrograph (in cubic feet) should equal 1” times the drainage area (in cubic feet).  Show calculations on excel spreadsheet.

 

c)     Graph the following on one graph (x-axis time: 0 to 15 hours)

 

 

Synthesize Unit Hydrographs using the Lagging Storm Method (Separate Excel TAB called “Lagging Storm”)

 

a)     Synthesize and graph a 4-hour unit hydrograph using the lagging storm method

 

Graph Unit Hydrographs (Separate TAB called “Unit Hydrograph-2 and 4 hr”)

 

On the same graph and using the same time increments (0-15 hours), graph the 2-hour and 4-hour unit hydrographs.  What is true about the area under the graphs?  How do the peak flows and time to peak flows compare to each other?  Place text boxes with answers.